1. Field of the Invention
The present invention relates to an asynchronous transfer mode (ATM) self-flow control system, and more particularly to a shaping function which is used for traffic control in a user terminal transmission end, an ATM network transmission and reception ends or an ATM network.
2. Description of the Related Art
As well-known, all data are handled as ATM cells with 53-byte fixed length in an ATM system. A control data header is 5 bytes of the 53 bytes and an information field for a user data (called a payload) is 48 bytes. In this way, in the ATM system, a data sequence with this fixed length (a packet) is used as a unit of multiplexing and exchanging. In the header are written a data VCI (virtual channel identifier) for identifying a connection to which the ATM cell belongs, a data VPI (virtual pass identifier), a data CLP (cell priority identifier) for indicating whether or not discard of the ATM cell is permissible when congestion is generated, a data PT (cell class identifier) for identifying network control information, and a data for functions such as header error detection/control (HEC).
Here, the connection indicates a route used to transmit the ATM cell between the users. The ATM cells having different identifiers are prepared for communication between different users. The identifier is called a connection number. The connection number contains the above data VCI and data VPI. Also, the CLP bit which is defined in the header is the bit which indicates a discard priority of the ATM cell, as described above. The data CLP=1 indicates that the ATM cell has a high discard priority, and the data CLP=0 indicates that the ATM cell has a low discard priority. In this specification, the ATM cell of CLP=0 is referred to as a normal ATM cell or a usual ATM cell, and the ATM cell of CLP=1 is referred to as a tagging ATM cell. The tagging ATM cell has a discard priority higher than the normal ATM cell and is always possible to be discarded. That is, the tagging ATM cell may be transmitted when the transmission route is empty, if it does not affect to other ATM cells.
By the way, since such ATM cells are randomly transmitted from a transmission side, the ATM cells are received as the reception ATM cells which are temporally dispersed on the reception side, as shown in FIG. 14A. Here, in FIGS. 14A, A, B, C, D and E indicate the ATM cells. As shown in FIG. 14A, because each of the ATM cells has different transmission rates, there is a case that a large time interval is between the adjacent reception ATM cells as in the ATM cells B and C. Also, there is a case that small time intervals are between the adjacent reception ATM cells as in the ATM cells C, D and E. If the time interval between the adjacent reception ATM cells is so small that a lump of ATM cells is formed such as the ATM cells C, D and E, the transmission rates of the ATM cells sometimes become higher than a predetermined transmission rate. Such a lump of ATM cells is called a burst ATM cell group and it is said that the burst degree is high as the time interval between the ATM cells becomes smaller.
In order to reduce the burst degree, an operation is performed to separate a reception ATM cell from another reception ATM cell immediately before the reception ATM cell (Hereinafter, to be merely referred to as a previous ATM cell) by a predetermined time interval or more. For this purpose, a delay buffer is used to delay a reception ATM cell by the predetermined time interval. The function to correct the transmission rate of the ATM cell in this way, in other words, the function to adjust an ATM cell time interval is called "traffic shaping" or simply "shaping" in this technical field. That is, in the shaping, as shown in FIG. 14B, the transmission rates of the reception ATM cells are corrected to have a predetermined value in accordance with a preset parameter (requested transmission rate). Therefore, because the above delay buffer is used for the shaping, the delay buffer is also called a shaping processing buffer.
FIG. 1 shows the structure of a conventional shaping processing apparatus. The conventional shaping processing apparatus is composed of a shaping processing buffer 10, an ATM cell identifying section 20', a scheduling section 30 and a mapping section 40'.
The shaping processing buffer 10 can receive read/write addresses A'.sub.W/R outputted from the mapping section 40' to be described later, randomly write the reception ATM cells Cr in accordance with the read/write address A'.sub.W/R, and sequentially read the written ATM cells as transmission ATM cells Ct.
The scheduling section 30 calculates a time interval between a previous ATM cell of the same connection and a current ATM cell based on shaping algorithm so that the reception ATM cell Cr can be transmitted in an ideal ATM cell time interval. The scheduling section 30 determines a necessary delay quantity based on the calculated time interval, and outputs a storage address As of the reception ATM cell indicating an ideal transmission time to the mapping section 40'.
The mapping section 40' performs the mapping of the reception ATM cell Cr as follows. That is, the mapping section 40' detects whether or not the area corresponding to the storage address is empty, based on the reception ATM cell storage address As supplied from the scheduling section 30. When another ATM cell is already mapped into the storage address area so that a conflict is generated, search processing is executed for an empty storage address area which is the nearest to the storage address area for the address in a direction behind the storage address area to determine a new storage address area for the reception ATM cell Cr in the shaping processing buffer 10. The mapping section 40' stores related information such as the connection number of the reception ATM cell Cr and the data CLP in the empty storage address area. Also, the mapping section 40' outputs the reception ATM cell write address to the shaping processing buffer 10.
The ATM cell identifying section 20' outputs the ATM cell identifying result R'.sub.ci in accordance with the connection number. The mapping section 40' receives this ATM cell identifying result R'.sub.ci. As shown in FIG. 2, the mapping section 40' is composed of a transmission time managing memory 41' having (n+1) addresses, for managing the empty address areas and the connection numbers when the mapping is performed, and an address managing section 42' for the transmission time managing memory 41'.
Next, the operation of the conventional shaping processing apparatus shown in FIG. 1 will be described.
Here, it is assumed that the ATM cell stream in which normal ATM cells and a lot of tagging ATM cells are mixed in a same band to have a relatively high burst traffic characteristic. In this case, the ATM cell identifying section 20' extracts the connection number of a reception ATM cell Cr from the header of the reception ATM cell Cr and transfers to the mapping section 40'. Also, at the same time, the scheduling section 30 determines the transmission time of the reception ATM cell Cr as follows. That is, the scheduling section 30 finds an ideal or theoretical transmission time of the reception ATM cell Cr from shaping algorithm calculation based on the arrival time of the reception ATM cell Cr, the transmission time of the previous ATM cell having the same connection number, and the transmission time interval of the transmission ATM cell which is previously set for the connection number. Then, the scheduling section 30 transmits the determined ideal transmission time to the mapping section 40'.
When receiving the above various types of information, the mapping section 40' refers to the transmission time managing memory 41' for managing the address information. Thus, the mapping section 40' checks whether the storage address area corresponding to the ideal transmission time of the reception ATM cell Cr is empty. The transmission time managing memory 41' manages a storage area corresponding to the ideal transmission time of the reception ATM cell Cr. When it is determined that the storage address area corresponding to the ideal transmission time of the reception ATM cell Cr is empty, the mapping section 40' outputs the connection number of the reception ATM cell Cr and this address information to the address area as a write address of the shaping processing memory 10.
Also, various conventional examples which relate to the present invention are proposed. For example, In Japanese Laid Open Patent Disclosure (JP-A-Heisei 6-216929: hereinafter, to be referred to as a first conventional example), an "ATM switch" is disclosed in which ATM cells which are centered to a specific input line are processed using memories which are even arranged for input lines. In the first conventional example, the ATM cell conflict control state of the whole ATM switch is estimated. In a congestion state, the number of ATM cells to be transmitted is suppressed, and in the empty state, a lot of ATM cells are transmitted. Alternatively, the arrival time of the ATM cell is recorded in the ATM cell, and the arrival time of the ATM cell is considered based on the recorded arrival time such that an ATM cell having a long waiting time is transmitted. In order to reduce the congestion state of the ATM cells, it is necessary that the arrival time and the transmission time of the ATM cell are managed for a conflict control. However, the object of the first conventional example is to attempt to improve the non-equality of ATM cell traffic by the buffer management of the ATM switch. Therefore, the first conventional example has no relation with the shaping function according to the present invention.
Also, in Japanese Laid Open Patent Disclosure (JP-A-Heisei 4-115643: to be referred to, hereinafter, as a second conventional example) corresponding to U.S. Pat. No. 5,267,232, a "method of controlling a data transmission in ATM network" is disclosed. In the second conventional example, a network control is achieved in a simple mode, when a plurality of discard priorities exist in one virtual channel. The method is composed of a step of separately declaring traffic characteristic of whether there are only discard non-permitted ATM cells or whether there are mixed discard permitted ATM cells and discard non-permitted ATM cells, and a step of estimating an ATM cell discard ratio based on the declared traffic characteristic to execute connection accept desk control (CAC) in the network. The ATM cell discard ratio is separated based on whether there are only discard non-permitted ATM cells or whether there are mixed discard permitted ATM cells and discard non-permitted ATM cells in the multiplexed virtual channel. The ATM cell discard ratio is guaranteed by the network based on the estimated ATM cell discard ratio.
It should be noted that the discard permitted ATM cell in the second conventional example and the discard non-permitted ATM cell are equivalent to the tagging ATM cell and the normal ATM cell or the usual ATM cell of the present invention, respectively. The second conventional example discloses the technique to guarantee an ATM cell discard ratio for every virtual channel. Therefore, the second conventional example has no relation with the shaping function according to the present invention, like the above first conventional example.
In the above-mentioned conventional shaping processing apparatus, in the memory conflict control system which has a general shaping function, the shaping processing is performed without being conscious of the tagging ATM cell. That is, all the reception ATM cells are handled equally as the normal ATM cell without identifying the tagging ATM cell.
In a case where the above conventional examples are used, the burst degree is estimated by a network administrator, and the ATM cell delay buffer is designed in such a manner that the shaping processing can be sufficiently performed. However, when a lot of tagging ATM cells are contained in the ATM cells in the same band, there is a case that the burst is generated so that the ATM cells are received over a permission value of the ATM cell delay buffer. In this case, therefore, there is a problem in that the reception ATM cells over this permission value has been consequently discarded.
In accordance with, in order to solve this, it is necessary to increase the permission value of the ATM cell delay buffer which is necessary for the process shaping. However, it is obscure that the problem passes away if the buffer has what quantity. Also, if the buffer quantity is increased, a new problem occurs in which the hardware scale increases.